Filtrationmust expand to improve blood safety

vCJD is a devastating and lethal brain disease with no cure, that is caused when prion proteins change shape and become “abnormal”. The disease was originally transmitted to humans through eating meat products contaminated with BSE. While strict measures were put in place to protect the human food chain from BSE in the early 1990s, it was quickly established that infectious prions could be passed between humans by way of blood transfusions or treatment with contaminated blood products. But is vCJD really still a threat? A cursory look at the number of victims might suggest not. According to the Edinburgh based vCJD Surveillance Unit a total of 168 people in the UK have died of the disease since 1990. However, these figures mask the growing concern that rising numbers of potential blood donors are incubating infectious prions while exhibiting no external symptoms. Dr Robert Rohwer, director of Molecular Neurovirology Laboratory and associate professor of neurology at the University of Maryland, recently presented to the Patient Safety 2010 Conference in London, stating that recent developments strongly support predictions of second and third waves of long incubation vCJD. He pointed to recent research by Professor John Collinge of the National Prion Clinic, published in the Lancet in December 2009, which described the first patient to succumb to vCJD from a previously unaffected genetic subgroup of the prion protein. Prior to this point, all 215 peo

ple who died of vCJD worldwide shared a certain version of the prion gene that is present in only one third of the population. The new finding strengthens an earlier prediction by Prof. Collinge of second and third waves of vCJD in people who were infected over the same period as people in the first wave, but whose genetics result in a longer incubation time. To date, at least five people have been confirmed as contracting vCJD after having received contaminated blood. Studies have shown that human to human transmission appears to be highly efficient – up to 100 times more so than between bovine and human. The most respected estimate of the prevalence of people incubating vCJD today is anywhere between 1 in 4,000 and 1 in 20,000 (from the Hilton study based on tests on tonsil and appendix samples), but due to challenges in detecting the disease, prevalence could be more widespread. The worry is that there is currently no way of knowing how many of those people will develop vCJD in their lifetime; the vast majority show no symptoms and the incubation period could be several decades. With that in mind, the UK Government introduced measures to protect against infection from contaminated blood. In particular, these focused on the way blood was gathered and treated. In addition to restricting certain high risk groups from donating blood, in 1998, leucodepletion was introduced by the UK blood services. The filtration process – which is still in place – removes white blood cells from blood destined for transfusion, but the result only provides between a 40% and 70% reduction in vCJD infectivity.

Protecting blood